1. Field of the Invention
The present invention is related to a method for preparing nano-scale platinum (Pt), and particularly to the method for preparing nano-scale platinum that uses removing water and increasing the concentration of a precursor solution through heating, such that the reduction of platinum would be accelerated so as to obtain the small particle-sized and uniformly-dispersed nano-scale platinum on carbon nanotubes (CNTs) with improved electrocatalytic preferential orientation facets and superior electrochemical properties.
2. Description of the Related Art
Currently, the depletion of natural resources and environmental protection have become urgent issues, and thus related scientists and researchers all over the world spare no effort to find feasible solutions for environmental pollution and alternative energy resources with high conversion efficiency. The principle of fuel cells converts chemical energy to electrical energy by using redox reactions. Compared with other kinds of environmental energies, fuel cells have the advantages of high conversion efficiency, strong mobility, adaption of various different fuels as well as free of pollution.
Due to the features of nano materials including small size, large specific surface area, high surface energy and high proportion of surface atoms, the metal nano materials are characterized in that the surface effects, small size effects and tunneling effects of nanotechnology can be applied extensively in different fields. Therefore, finding a way of preparing nano materials with a homogeneous and large surface area efficiently becomes an important subject for scientists. For fuel cells, platinum is mainly used as a catalyst in an electrochemical reaction. In prior art, nano-scale platinum is prepared by a hermetic reflux system. As shown in FIG. 1, the hermetic reflux system 1 comprises a flask 11, a condenser 12 and a pressure regulator 13. Platinum salt, a reducing agent and deionized water are mixed to form a precursor solution in the flask 11. The precursor solution in the flask 11 is heated at a predetermined temperature (such as 160° C.). Then, the water in the precursor solution boils and evaporates to become water vapor by the heating process. The water vapor is passed into the inner tube of the condenser 12 and cooled and condensed into a liquid by a cooling substance which flows into the condenser and around the outside of the inner tube. Pressure generated during the water evaporation process can be controlled by the pressure regulator 13 mounted on the system. Next, the liquid in the condenser 12 is returned to the flask 11 to maintain the water content in the precursor solution. At the same time, the nano-scale platinum in the precursor solution in the flask 11 is gradually reduced on the carbon nanotubes.
However, the preparation of the nano-scale platinum using the conventional hermetic reflux system takes about 4 hours and requires a hermetic system with the pressure regulation function. Currently, superior electrochemical properties of the prepared nano-scale platinum used as an electrode catalyst in fuel cells are required in a time-efficient way. Therefore, it is necessary to develop a simplified method for preparing nano-scale platinum with small size, highly homogeneous distribution, enhanced electrocatalytic preferential orientation facets and superior electrochemical properties to solve the problems of a long preparation time, a complicated reduction system and poor electrochemical properties of the platinum electrode catalysts.